Mainframes, super computers, mass storage systems, workstations and very high resolution display subsystems are frequently connected together to facilitate file and print sharing. Common networks and channels used for these types of connections oftentimes introduce communications bottlenecking, especially in cases where the data is in a large file format typical of graphically-based applications.
There are two basic types of data communications connections between processors, and between a processor and peripherals. A "channel" provides a direct or switched point-to-point connection between communicating devices. The channel 's primary task is merely to transport data at the highest possible data rate with the least amount of delay. Channels typically perform simple error correction in hardware. A "network," by contrast, is an aggregation of distributed nodes (e.g., workstations, mass storage units) with its own protocol that supports interaction among these nodes. Typically, each node contends for the transmission medium, and each node must be capable of recognizing error conditions on the network and must provide the error management required to recover from the error conditions
One type of communications interconnect that has been developed is Fibre Channel. The Fibre Channel protocol was developed and adopted as the American National Standard for Information Systems (ANSI). See Fibre Channel Physical and Signalling Interface, Revision 4.2, American National Standard for Information Systems (ANSI) (1993) for a detailed discussion of the fibre channel standard. Briefly, fibre channel is a switched protocol that allows concurrent communication among workstations, super computers and various peripherals. The total network bandwidth provided by fibre channel is on the order of a terabit per second. Fibre channel is capable of transmitting data frames at rates exceeding 1 gigabit per second in both directions simultaneously. It is also able to transport existing protocols such as internet protocol (IP), small computer system interface (SCSI), high performance parallel interface (HIPPI) and intelligent peripheral interface (IPI) over both optical fiber and copper cable.
Essentially, fibre channel is a channel-network hybrid, containing enough network features to provide the needed connectivity, distance and protocol multiplexing, and enough channel features to retain simplicity, repeatable performance and reliable delivery. Fibre channel allows for an active, intelligent interconnection scheme, known as a "fabric," to connect devices. A fabric is an entity that interconnects various network elements or "node-ports" (N.sub.-- ports), attached to the fabric. The fabric has the capability of routing data frames based upon information contained within the frames as specified by a class of service. The N.sub.-- port simply manages the simple point-to-point connection between itself and the fabric. That transmission is isolated from the control protocol so that different topologies (e.g., point-to-point links, rings, multidrop buses, crosspoint switches) can be implemented. The fabric is self-managed so that N.sub.-- ports do not need station management functionality, greatly simplifying system implementation.
The Fibre Channel industry standard provides for several different types of data transfers. A class 1 transfer, which requires a dedicated circuit-switched connection between N.sub.-- ports, involves the transfer of at least one data frame, and often numerous data frames, between N.sub.-- ports. A class 2 transfer, which is directed to connection-less, frame switching between N.sub.-- ports, typically involves only a single data frame being transferred from one N.sub.-- port to another N.sub.-- port. Class 2 service provides guaranteed delivery and receipt confirmation. Class 2 requires processing of overhead with every frame that is transferred (i.e., each data frame has an associated header field that needs to be processed before the payload, or data, is actually transferred), whereas class 1 data transfer handles overhead up front with the first frame only. A class 3 transfer is similar to the class 2 transfer, except that class 3 transfers do not provide receipt confirmation.
An optional mode of data transfer that provides some of the functionality of both class 1 and class 2 service is known as intermix. Intermix reserves a separate, low priority data path that is accessible to all N.sub.-- ports, and permits connection-less traffic, such as a class 2 data transfer, to be interjected into a continuous stream of class 1 data if the appropriate bandwidth is available during idle time.